Centrifugal solids deliquefying and treating process and apparatus



1967 .YAsuo KOWATA ENTRIF'UGAL SOLIDS DELIQUEFYING AND TREATING PROCESS AND APPARATUS 2 Sheets-Sheet 1 Filed Feb. 21., 1964 1 NVEN TOR.

YASUO KOWATA ATTORNEY F I, 1967 YASUO KOWATA 3,302,873

CENTRIFUGAL SOLIDS DELIQUEFYING AND TREATING PROCESS AND APPARATUS Filed Feb. 21, 1964 2 Sheets-Sheet 2 w INVENTOR YASUO KOWATA ATTORNEY United States Patent 3 302 873 QENTREFUGAL SULEDEDELEQUEFYING AND TREA'HNG FROCEES AND APPARATUS Yasuo Kowata, Tokyo, lapan, assignor to Pennsait Chemicais Corporation, Phiiadelphia, Pa, 21 corporation of Pennsylvania Filed Feb. 2t, 1964, Ser. No. 346,507 6 Claims. (Cl. 233--7) This invention relates to centrifuges. More specifically this invention relates to means for improving the purity of solids discharged from a continuous solids discharge centrifuge. Still more specifically this invention relates to provision for effecting a rinse of the solids prior to their discharge from a centrifuge.

Continuous solids discharge centrifuges are old in the art. Illustrative of these is that type of centrifuge commonly called a worm centrifuge and comprising a solids bowl containing a screw conveyor. It has means for driving the bowl and conveyor at different speeds to effect a scrolling of the solids up the beach out of the pond of slurry and toward the solids discharge port of the bowl. An example is shown, for instance, in the US. Patent 2,703,676, which issued March 8, 1955, on an application by F. P. Gooch.

It frequently occurs that in the separation of solids from a slurry in such a centrifuge it is desirable to have the deliquefied solids discharge at the highest possible purity. For instance in the separation of ammonium sulfate solids from their mother liquor the traces of am monia in the mother liquor are desirably removed from the solids prior to the discharge of the solids. Conventionally the removal of the traces is accomplished by a rinse which is normally accomplished by a rinse tube and nozzle disposed substantially on the axis of the machine and spraying a rinse liquid outward onto the solids as they approach the solids discharge. The ethciency of such a rinse is in some cases, however, not sufiiciently high and it has been necessary to reslurry the discharge solids in a rinse tank and once again deliquefy them.

I have found after much experimentation that a major reason why the former method of rinsing in continuous solids centrifuges is not of great efficiency is because the rinse liquid has contacted only the surfaces of the solids exposed to the rinse nozzle and has then moved along the surface of the built-up solids and down into the pond. In other words, the solids have not been permeated and thoroughly contacted on all their sides by the rinse liquid. The discharging solids have thus contained a high amount of the mother liquor.

I have developed means by which a rinse more elficient than the prior rinses is possible. Briefly I direct rinse liquid toward the solids not from adjacent the axis of the centrifuge in an outward direction but from adjacent the periphery of the centrifuge in an inward direction. The rinse is thus delivered deep into the built-up solids layer. Since this form of rinsing may effectively cominence while the solids are still submerged in the pond, the solids enjoy a longer rinse period. As the rinse liquid moves inward it displaces traces of mother liquor on the solids. The traces move into the pond, and thus solids of higher purity discharge from the bowl.

Other objects and features of the invention will be apparent to those skilled in the art upon reading the more complete description of an embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a fragmentary sectional view in somewhat simplified fashion of a centrifuge embodying the invention;

FIGURE 2 is a fragmentary section taken on the line 2-2 of FIGURE 1;

FIGURE 2a is an enlarged fragmentary sectional view taken on the line 2a-2a of FIGURE 2;

FIGURE 3 is a fragmentary enlarged sectional view of an apparatus embodying the invention and showing the use of rinse on settled submerged solids;

FIGURE 4 is a fragmentary sectional view of an apparatus embodying the invention and showing operation of the rinse on the beach approaching the solids discharge port; and

FIGURE 5 is a view comparable to FIGURE 4 but showing the operation of rinse in a prior art machine.

Referring more specifically to the drawings, an apparatus embodying the invention is partially shown in sec tion in FIGURE 1 and designated Hi. It comprises the bowl 112 and the conveyor 14 which are driven at slightly different speeds by means not shown. The bowl 12 includes an inwardly inclined portion or beach to towards the inner end of which is provided a solids discharge opening 18.

The conveyor 14 is provided with a helical flight or flights 29 which extend outwardly substantially perpendicular to the adjacent portion of the bowl wall. In rotat ing at a speed slightly different from the bowl the conveyor flight 2t conveys by screw action the solids along the bowl wall, up the beach In and finally out the solids discharge opening 18.

Disposed along the axis of the machine is a feed tube 22 adapted to deliver feed slurry to the interior of the conveyor from which it discharges through feed nozzle or opening 24 into the bowl. The slurry thrown out against the wall of the bowl by centrifugal force forms a pond having a level determined by the liquid discharge outlet (not shown) usually at the opposite end of the bowl from the solids discharge opening.

Solid rinse liquid is supplied to the conveyor through a rinse tube as which may surround the feed tube 22 thus forming an annular passage. The rinse liquid discharges into the conveyor through an opening 28 in the rinse tube. An essential of the invention is that the rinse liquid is delivered to the bowl adjacent its periphery. In the embodiment shown the delivery point is adjacent the distal edge of the conveyor. This is effected through passage means which include ports 3t) through the conveyor wall and also chamber Stla in the conveyor iiight 20 and terminate in openings 32 on the leading face of the flight adjacent its distal edge. To reduce the likelihood of the openings 32 being plugged by solids, the portion 34 of the flight edge from. the openings to the extreme margin of the flight may be beveled in the area of the openings. As shown (FIG. 2) the openings 32 may be widened in a direction opposite the direction of rotation to ease the rinse liquid out into the bowl and avoid excessive turbulence.

The number of openings 32 provided in the conveyor flight 20 may be varied. It is desired, however, to provide sufficient number of openings to promote even distribution of the rinse so that the discharging solids are characterized by a more or less uniform degree of purity. The openings may be fed by individual passages from the interior of the conveyor instead of by a chamber Mia if desired or necessary.

In the operation of the embodiment shown, feed liquid is delivered through the feed tube 22 out opening 24 and into the pond. The solids acted on by centrifugal force form a layer against the wall of the bowl and are moved toward the right (FIG. 1) and the discharge opening 18 by the conveyor flight 2%. Rinse liquid is introduced by the rinse tube 26 through opening 28 through passage means including ports 30 and chamber 30a and is discharged through openings 32 into the deep part of the solids layer. Prior to the action of the rinse the interstices between the solids a (FIG. 3) are filled with the mother liquor having entirely the same chemical and physical properties as the liquid of the feed. The rinse liquid discharging through the openings 32 displace the mother liquor in the interstices progressively outward from the openings so that the mother liquor is forceably ejected back into the pond.

As the rinse liquid diffuses through the solids layer ahead of the flight it eventually reaches the solids-liquid interface by which time substantiflly all of the mother liquor has been replaced by rinse. This action continues even as the solids are moved up the beach 16 (FIG. 4). The result is that the rinse liquid which originally replaced the mother liquor in the interstices is in turn replaced by a new supply of rinse liquid of even greater purity. This progressively diminishes the traces of the mother liquor which remain on the solids.

Because the rate of rinse liquid is selected to be adequate to keep liquid inward of the passage from the level of the pond, hydrostatic pressure urges the rinse liquid into movement through the openings 32. Alternatively the rinse liquid can be supplied to the passage means and openings 32 through pressure fittings from a pressure source. From a reference to FIG. 5 the reason for improved eficiency of the rinse in accordance with the present invention will be understood. Accord ing to prior rinse systems the rinse liquid was delivered to the solids only after they had been moved out of the pond and up the beach 16' by the flight 2d. The rinse liquid was supplied from a nozzle 100 disposed in the body of the conveyor 14' and supplied through a rinse tube similar to that illustrated in FIGURE 1. Because the solids were tightly packed by the flight the rinse liquid was not able to permeate the solids layer sufficiently. The rinse therefore moved along the surface of the solids layer back down and around into the pond. Below the surface of the solids layer the interstices of the solids I) remained filled with mother liquor c and the solids were discharged from the centrifuge with relatively high amounts of impurity. In addition to this the rinse period was relatively short; only extending from emergence of the solids from the pond to their discharge. Rinsing in the pond was impossible. Because of this inefliciency it was often necessary to reslurry the solids and re-centrifuge.

In accordance with the present invention a high degree of efliciency in rinsing is obtained. An essential feature of the invention is the delivery of the rinse to the deep part of the solids layer. This makes possible not only a commencing of the rinsing while the solids are still submerged in the pond, but also more effective permeating of the solids in the pond and on the beach. While embodiments of the invention offer greatly improved rinsing they involve simple and inexpensive modification to equipment.

It is, of course, envisioned that rather than a rinse liquid a liquid of character that reacts with the solids may be supplied to the solids by the means of the invention disclosed. In such application the means of the invention will promote more uniform reaction than hereitofore achieved by the conventional rinse spray nozzle.

Therefore, having particularly described my invention, it is to be understood that this description is by way of illustration, and that changes, omissions, additions, substitutions, and/or other modifications may be made without departing from the spirit and scope of the claimed invention.

I claim:

1. A centrifuge for separating liquids and solids comprising a bowl having an imperforate peripheral wall, a helical conveyor element mounted within and coaxial of said bowl, means for rotating the bowl and conveyor element at diflerent speeds, means for feeding slurry to the bowl, the bowl being formed with a solids discharge port, a liquid discharge port and an inwardly inclined wall portion approaching said solids discharge port from the direction of the liquid discharge port, the helical conveyor element having flight portions with distal edges adjacent the peripheral wall of the bowl, the conveyor element having passage means through said portions and openings for said passage means adjacent the distal edges in the area of the inwardly inclined wall portion and at a radius greater than the radius of said liquid discharge port, means for feeding a treating liquid to the passage means, whereby treating liquid can be eifectively delivered to the deep portion of the solids layer engaged by the flight portions while the solids are still submerged and as the solids approach the solids discharge port.

2. A centrifuge as described in claim 1 wherein the openings in the flights of the conveyor element are on the leading face thereof.

3. A centrifuge as described in claim 11 wherein the edges of the leading face flights portion adjacent the openings are bevelled.

4. A centrifuge as described in claim 1 wherein a portion of the wall of the passage means adjacent the openings are slanted in a direction opposite the direction of conveyor element rotation.

5. A process for centrifugal separation including the steps of introducing a liquid-solids feed to a zone of centrifugation, permitting the solid to settle to the periphery of the zone, injecting from adjacent the periphery of the zone a treating liquid into the solids while the solids are submerged in the feed liquid, engaging the solids with a conveying surface, moving the solids inward out of the feed liquid and permitting the treating liquid to drain from the solids back into the feed liquid, discharging the treated solids and separately discharging the separated feed liquid.

6. The process as described in claim 5 wherein the treating liquid is a rinse liquid.

References (Cited by the Examiner UNITED STATES PATENTS 581,354 4/1897 Lapp.

992,876 5/1911 Jones 2337 1,064,184 6/1913 Wels 2337 2,308,559 1/1943 Winkler 233-7 XR 2,685,369 8/1954 Crossley 23314 XR FOREIGN PATENTS 698,750 10/1953 Great Britain.

M. CARY NELSON, Primary Examiner.

HENRY KLINKSIEK, Assistant Examiner, 

1. A CENTRIFUGE FOR SEPARATING LIQUIDS AND SOLIDS COMPRISING A BOWL HAVING AN IMPERFORATE PERIPHERAL WALL, A HELICAL CONVEYOR ELEMENT MOUNTED WITHIN AND COAXIAL OF SAID BOWL, MEANS FOR ROTATING THE BOWL AND CONVEYOR ELEMENT AT DIFFERENT SPEEDS, MEANS FOR FEEDING SLURRY TO THE BOWL, THE BOWL BEING FORMED WITH A SOLIDS DISCHARGE PORT, A LIQUID DISCHARGE PORT AND AN INWARDLY INCLINED WALL PORTION APPROACHING SAID SOLIDS DISCHARGE PORT FROM THE DIRECTION OF THE LIQUID DISCHARGE PORT, THE HELICAL CONVEYOR ELEMENT HAVING FLIGHT PORTIONS WITH DISTAL EDGES ADJACENT THE PERIPHERAL WALL OF THE BOWL, THE CONVEYOR ELEMENT HAVING PASSAGE MEANS THROUGH SAID PORTIONS AND OPENINGS FOR SAID PASSAGE MEANS ADJACENT THE DISTAL EDGES IN THE AREA OF THE INWARDLY INCLINED WALL PORTION AND AT A RADIUS GREATER THAN THE RADIUS OF SAID LIQUID DISCHARGE PORT, MEANS FOR FEEDING A TREATING LIQUID TO THE PASSAGE MEANS, WHEREBY TREATING LIQUID CAN BE EFFECTIVELY DELIVERED TO THE DEEP PORTION OF THE SOLIDS LAYER ENGAGED BY THE FLIGHT PORTIONS WHILE THE SOLIDS ARE STILL SUBMERGED AND AS THE SOLIDS APPROACH THE SOLIDS DISCHARGE PORT. 